Oxide sintered body

ABSTRACT

An oxide sintered body is composed mainly of indium and containing tungsten, has a resistivity of no more than 1 kΩcm. The tungsten content in terms of the W/In atomic ratio is preferably at least 0.001 and no more than 0.17. The oxide sintered body comprise mainly a bixbyite structure indium oxide crystal phase containing tungsten in a solid solution and/or an indium tungstate compound crystal phase, with no tungsten oxide crystal phase present, whereby an oxide sintered body for use as a sputtering target is provided, for an oxide based transparent conductive film with low resistance and excellent transmission characteristics for the infrared light region.

PRIORITY CLAIM

This application is a Continuation of U.S. Ser. No. 10/441,980 filed May20, 2003, now allowed and claims priority from Japanese ApplicationNumber 2002-255425 filed Aug. 30, 2002, the contents of which are hereinincorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an oxide sintered body for use as asputtering target or an ion plating tablet when manufacturing a lowresistance oxide based transparent conductive film used in solar cellsand liquid crystal display elements and the like by a sputtering methodor an ion plating method, and relates specifically to an oxide sinteredbody for use as a sputtering target and as an ion plating tablet used toform a transparent conductive film which has a high transmittance in theinfrared region, and low resistance, for use in a solar cell.

PRIOR ART

Oxide based transparent conductive films have both high conductivity,and high transmittance of the visible light spectrum. Consequently,oxide based transparent conductive films are used not only as theelectrodes in solar cells, liquid crystal display elements, and variousother photodetectors, but due to their reflection and absorptioncharacteristics for near infrared wavelengths, are also used as heatreflecting films for car window glass or building window glass, as avariety of antistatic coatings, and as transparent heating elements fordefogging freezing display cases and the like.

Widely used varieties of oxide based transparent conductive filmsinclude tin oxide (SnO₂) films containing antimony or fluorine as adopant, zinc oxide (ZnO) films containing aluminum or gallium as adopant, and indium oxide (In₂O₃) films containing tin as a dopant.Indium oxide films which contain tin as a dopant, that is In₂O₃—Sn basedfilms, are referred to as ITO (Indium Tin Oxide) films, and have beenwidely used because of the ease with which a low resistance oxide basedtransparent conductive film can be obtained.

Frequently used methods for manufacturing the oxide based transparentconductive films mentioned above include sputtering methods and vapordeposition methods, ion plating methods, and methods involving theapplication of a coating for forming a transparent conductive layer. Inparticular, sputtering methods and ion plating methods are effectivewhen using a material with low vapor pressure, or when precise controlof the film thickness is required, and are widely used industriallybecause of their extreme ease of operation.

In a sputtering method, generally a film is formed by causing a glowdischarge to occur between a substrate acting as the anode, and asputtering target of a raw material for forming an oxide basedtransparent conductive film acting as the cathode, under an argon gaspressure of no more than approximately 10 Pa, to generate argon plasma,and then causing the positive argon ions within the plasma to strike thecathode target, thereby ejecting particles of the target component, andcausing these particles to be deposited on the substrate.

Sputtering methods are classified according to the method used togenerate argon plasma, and those methods which use RF plasma are calledRF sputtering methods, while those using direct current plasma arecalled DC sputtering methods. DC sputtering methods are more widely usedindustrially due to their faster deposition rates, cheaper powersupplies and simpler deposition operation than RF sputtering methods.However, although a nonconductive sputtering target can be used with anRF sputtering method, with a DC sputtering method, a conductivesputtering target must be used.

Furthermore, the deposition rate of a sputtering method is closelyrelated to the chemical bonds of the materials which constitute thesputtering target. In other words, because sputtering involves aphenomenon in which positive argon ions with kinetic energy are made tostrike the surface of the cathode sputtering target, causing a portionof the sputtering target which receives this energy to be sputtered fromthe target surface, the weaker the bonds between ions or the bondsbetween atoms of the materials which constitute the sputtering target,the higher the rate of sputtering caused by the ions striking thetarget.

On the other hand, looking now at solar cells in which the oxide basedtransparent conductive films are used, these solar cells comprise p-typeand n-type semiconductors in a layered structure, and are broadlyclassified according to the type of semiconductor. The most commonlyused type of solar cell uses silicon, which is both safe, and abundantin terms of natural resources. There are three types of solar cellsusing silicon, those using single cell silicon, polysilicon andamorphous silicon. Furthermore, development is proceeding in the fieldof solar cells known as compound thin film solar cells, which usecompound semiconductors such as CuInSe₂, GaAs and CdTe and the like.

However, regardless of the type of solar cell, it is essential that anoxide based transparent conductive film is provided as an electrode onthe side of the solar cell which is exposed to light, andconventionally, an ITO film, or a zinc oxide (ZnO) film doped withaluminum or gallium or the like, has been used. Properties required ofthese oxide based transparent conductive films are low resistance andhigh transmittance of sunlight.

As disclosed in Japanese Patent Application No. 2002-200534 by theinventors of the present invention, recently it became apparent, basedon research carried out by the inventors, that crystalline oxide basedtransparent conductive films composed mainly of indium, and containingeither tungsten, or tungsten and tin, are useful as the transparentelectrodes for a solar cell. These oxide based transparent conductivefilms not only have low resistance and excellent light transmissioncapability for the visible light spectrum, but also have excellent lighttransmission capability for the infrared spectrum when compared toconventionally used ITO films and zinc oxide films, and therefore usingsuch an oxide based transparent conductive film as the surface electrodeof a solar cell also enables the effective use of infrared light energy.

Furthermore, as disclosed in Japanese Patent Application No. 2002-157568by the inventors of the present invention, it became apparent that anamorphous oxide based transparent conductive film composed mainly ofindium and containing tungsten is useful as a transparent electrode fordisplay devices such as organic EL displays. Particularly when used as atransparent electrode for organic EL displays, because an extremely thinfilm of an organic compound is formed thereon, if the transparentelectrode has a high degree of surface unevenness, then leak damage ofthe organic compound occurs. Because these amorphous oxide basedtransparent conductive films have both low resistance and excellentsurface smoothness, they are useful as a transparent electrode for usein such cases when surface smoothness is required.

Furthermore, as disclosed in Japanese Patent Application No. 2002-211678by the inventors of the present invention, it became apparent that athin film layered product comprising an amorphous indium oxide filmcontaining tungsten and a metallic conductive film layer has excellentsurface smoothness and a sheet resistance of 1 to 5 Ω/□ even at filmthicknesses between 100 and 150 nm, and also has excellent transparency,and is therefore useful in high definition or large scale LCDs or as atransparent electrode for organic EL displays. The indium oxide filmcontaining tungsten in the thin film product with the above structure isan amorphous film formed by a sputtering method, which being formed onthe surface of the metallic conductive film layer, protects the metallicconductive film layer.

The oxide based transparent conductive film composed mainly of indiumand including either tungsten or tungsten and tin is manufactured usinga DC sputtering method, which is widely used industrially, but in termsof productivity and cost reduction, it is necessary for deposition to beachieved quickly. However, because it was not possible to obtain asputtering target which could be used to deposit these oxide basedtransparent conductive films, and which had a crystalline structureenabling the deposition rate of the sputtering method to be improved, itwas impossible to perform deposition at fast speeds.

Furthermore, the manufacture of these oxide based transparent conductivefilms using an ion plating method is also being investigated.

SUMMARY OF THE INVENTION

In accordance with the above circumstances, an object of the presentinvention is to provide an oxide sintered body for use as a sputteringtarget or an ion plating tablet which is capable of depositing quicklyan oxide based transparent conductive film which has low resistance andhigh transmittance for both the visible region and the infrared region,using a DC sputtering method.

An object of the present invention is to provide an oxide sintered bodyfor use as a sputtering target or an ion plating tablet which enablesthe manufacture of an oxide based transparent conductive film with lowresistance and excellent transmission characteristics for the infraredlight region, and for which fast deposition is possible.

PREFERRED EMBODIMENTS OF THE INVENTION

An embodiment of the present invention is an oxide sintered bodycomposed mainly of indium and containing tungsten, which has aresistivity of up to 1 kΩcm.

In addition, the resistivity is preferably up to 50 Ωcm, more preferablyup to 1 Ωcm, more preferably up to 1×10⁻² Ωcm or more preferably up to1×10⁻³ Ωcm, and the tungsten content is preferably at a W/In atomicratio of at least 0.001, and no more than 0.17. In addition, the oxidesintered body of the present invention preferably comprises mainly abixbyite structure indium oxide crystal phase containing tungsten in asolid solution, and/or an indium tungstate compound crystal phase, andcontains no tungsten oxide crystal phase.

Another embodiment of the oxide sintered body of the present inventionis an oxide sintered body composed mainly of indium, and containingtungsten and tin, which has a resistivity of no more than 1 kΩcm.

In addition, the resistivity is preferably no more than 60 Ωcm, morepreferably up to 1 Ωm, more preferably up to 1×10⁻² Ωcm or morepreferably up to 1×10⁻³ Ωcm, and the tungsten content is preferably at aW/In atomic ratio of at least 0.001, and no more than 0.17, and the tincontent is preferably at a Sn/In atomic ratio of at least 0.001, and nomore than 0.15. In addition, the oxide sintered body of the presentinvention preferably mainly comprises a bixbyite structure indium oxidecrystal phase containing tungsten and tin in a solid solution, and/or anindium tungstate compound crystal phase, and/or an indium stannatecompound crystal phase, and does not contain an tungsten oxide crystalphase.

The inventors of the present invention prepared oxide sintered bodiescomposed mainly of indium and containing tungsten (indium oxide sinteredbodies) under various manufacturing conditions, and performed sputteringdeposition without heating the substrate, using the oxide sinteredbodies as the sputtering target, and using the same gas pressure, typeof deposition gas, distance between the target and the substrate,deposition DC power and film thickness for each, and then measured theircharacteristics. These experiments and tests showed that the depositionrate of the DC sputtering method depends on the resistivity of the oxidesintered body used as the sputtering target, and that in the case of anoxide sintered body composed mainly of indium and containing tungsten,fast deposition rates can be realized if the resistivity is up to 1kΩcm, and preferably no more than 1×10² Ωcm.

Furthermore, the resistivity of the oxide sintered body can be loweredby subjecting the oxide sintered body to a reduction process by heatingin a non-oxidative atmosphere such as nitrogen. However, the resistivityof an oxide sintered body composed mainly of indium and containingtungsten depends on the form of the tungsten, and specifically, whentungsten oxide is present in the oxide sintered body, it is difficultfor the resistivity of the oxide sintered body to be lowered effectivelyby the reduction process.

Furthermore, the tests and experiments performed by the inventors of thepresent invention showed that of oxide sintered bodies which arecomposed mainly of indium and contain tungsten, the use of an oxidesintered body comprising a bixbyite structure indium oxide crystal phasecontaining tungsten as a solid solution, and/or an indium tungstatecompound crystal phase, and having no tungsten oxide crystal phasepresent, allows a higher deposition rate under the same conditions thanthe case in which an oxide sintered body in which a tungsten oxidecrystal phase can be detected is used, even if the resistivity is thesame. This finding is assumed to be because the sputtering rate of atungsten oxide crystal phase is slow.

A bixbyite structure is a type of indium oxide (In₂O₃) crystalstructure, and is also called a C-rare earth oxide type structure(“Transparent Conductive film Technology”, Ohm Co., 1999, p.82). Inaddition to the bixbyite structure, In₂O₃ can also take the form of acorundum structure. Positive ions such as tungsten and tin aresubstituted for the indium position of the bixbyite structure indiumoxide to form a solid solution.

Furthermore, an example of the indium tungstate compound is the InW₃O₉compound disclosed in JCPDS card 33-627, for example. Even if there areslight differences in composition from the stoichiometric composition,or the partial substitution of other ions occurs, provided that thecrystal structure is maintained, it remains within the scope of thiscompound.

According to the experiments performed by the inventors of the presentinvention, the same tendencies described above were observed for anindium tungstate compound containing tin.

The form of tungsten in an oxide sintered body composed mainly of indium(an indium oxide sintered body) varies according to the size of thetungsten oxide particles in the raw material from which the oxidesintered body is made, and the reduction process performed on thesintered body. In other words, if the average particle size of thetungsten oxide particles in the raw material is up to 1 μm, then indiumoxide tends not to be produced within the sintered body, and theresistivity of the sintered body is low. Furthermore, even if tungstenoxide is present in the sintered body, if the average particle size ofthe tungsten oxide particles in the raw material is within a range from3 μm to 5 μm, then the resistivity of the sintered body is reduced towithin acceptable levels by the reduction process.

As described above, it was apparent that an oxide based transparentconductive film deposited using an oxide sintered body containingtungsten as a sputtering target is useful as the transparent electrodefor a solar cell, for the following reasons.

When manufacturing an oxide based transparent conductive film which isdeposited using as the sputtering target an oxide sintered body obtainedby including tungsten, the tungsten with a valency of between four andsix occupies the indium position which has a valency of three as anionized impurity, causing carrier electrons to be released, andconductance to increase. Generally, an increase in ionized impurities inan n-type semiconductor such as indium oxide results in an increase inthe number of carrier electrons, but also results in a reduction in themobility of the carrier electrons due to ionized impurity scattering.However, if tungsten is added to the indium oxide in the form of ionizedimpurities, the number of carrier electrons can be increased withoutgreatly reducing their mobility. Accordingly, because the inclusion oftungsten allows the number of carrier electrons to be increased slightlywith the mobility of the carrier electrons remaining high, an oxidebased transparent conductive film which has low resistance and highinfrared light transmittance can be realized. This is the main reasonfor including tungsten in the present invention.

In order to prepare an oxide based transparent conductive film withresistance low enough to be practical, the tungsten in the target ispreferably at a W/In atomic ratio of between 0.001 and 0.17. If the W/Inatomic ratio is less than 0.001, no effect can be perceived, and atgreater than 0.17, the reduction in mobility due to impurity scatteringis significant, causing the resistance to rise.

Furthermore, a different embodiment of the present invention containsboth tin and tungsten. When an oxide based transparent conductive filmis prepared using this type of oxide sintered body as the sputteringtarget, the indium position which has a valency of 3 is occupied by tinwith a valency of 4 and tungsten with a valency between 4 and 6, causingcarrier electrons to be released, and conductance to increase. Theobjects and effects of the inclusion of tungsten are the same as above.The reason for including tin is that the same effects as above can beobtained when the increase in carrier electrons is supplemented byadding tin in addition to tungsten, with the mobility of the carrierelectrons remaining high.

In order to prepare an oxide based transparent conductive film with lowresistance and excellent transmission characteristics for both thevisible light spectrum and the infrared spectrum, the target or tabletpreferably contains an amount of tungsten at a W/In atomic ratio between0.001 and 0.17, and contains an amount of tin at a Sn/In atomic ratiobetween 0.001 and 0.15. If the amount of tin is less than 0.001, thenadding tin has no effect, and if greater than 0.15, the reduction inmobility due to impurity scattering is significant, causing theresistance to rise.

Accordingly, by using a sputtering target or ion plating tablet preparedfrom an oxide sintered body of the present invention, a low resistanceoxide based transparent conductive film with good light transmissioncapability in both the visible light region and the infrared lightregion, or a low resistance transparent conductive film with a smoothsurface, can be manufactured by a sputtering method or an ion platingmethod more quickly than has been conventionally possible.

EXAMPLES

The present invention is described more specifically below usingexamples.

An Oxide Sintered Body Composed Mainly of Indium and Containing Tungsten

Examples 1 to 4 The Effect of Average Particle Diameter

Using In₂O₃ powder with an average particle diameter of up to 1 μm andWO₃ powder with an average particle diameter of up to 1 μm as the rawmaterial powders, mixtures of In₂O₃ powder and WO₃ powder containingeach component at predetermined ratios were prepared to provide theatomic ratios shown in Table 1. Each mixture was placed in a resin pot,and mixed in a wet ball mill. At this time, a hard ZrO₂ ball was used,and the mixing time was set to 18 hours. After mixing had completed, theresulting slurry was removed and filtered, dried and crushed.

The crushed substance was then molded by applying 294 MPa (3 ton/cm²) ofpressure in a cold isostatic press.

Next, the molded product was sintered in the following manner. Using anatmosphere in which oxygen is introduced into the air in the sinteringfurnace at a rate of 5 liters/minute per 0.1 m³ of furnace capacity,sintering was performed for 3 hours at 1100□. In this case, thetemperature was raised at a rate of 1 □/minute, and during cooling aftersintering, the introduction of oxygen was halted and cooling to 1000□was conducted at a rate of 10□/minute.

On crushing the thus obtained coarse oxide sintered bodies andperforming X-ray powder diffraction measurements, it was observed that adiffraction peak caused by the crystal phase of a bixbyite structure waspresent in the oxide sintered bodies of examples 1 to 4, and that adiffraction peak caused by a InW₃O₉ phase disclosed in JCPDS card 33-627was also present in examples 2 to 4, but no diffraction peak caused byWO₃ or WO₂ was observed in any of the examples 1 to 4. Furthermore, itwas apparent from EPMA analysis that tungsten was present in the indiumoxide phase as a solid solution.

Each obtained oxide sintered body was processed to a diameter of 152 mmand a thickness of 5 mm, the sputtering surface was polished by a cupgrindstone, and the resistivity of the sputtering surface of the oxidesintered body was measured using the four-point probe method.

The results are shown in Table 1. The resistivity of the oxide sinteredbodies was between 0.5 kΩm and 1 kΩcm.

In addition, each processed oxide sintered body was bonded to a backingplate made of oxygen free copper using metallic indium, to produce asputtering target.

Next, the sputtering target was attached to a non-magnetic targetcathode in a DC magnetron sputtering system, and a glass substrate wasprovided in parallel to the target in a position opposing the target.The section of the glass substrate which faced the center of thesputtering target was marked with a marker pen. The distance between thetarget and the substrate was set to 60 mm, pure argon gas was mixed with1% oxygen gas and introduced to obtain a gas pressure of 0.5 Pa, a DCplasma was generated at 160W DC, and with the substrate and thesputtering target remaining in static opposition and without heating thesubstrate, DC sputtering was performed for 30 minutes. Furthermore, inorder to evaluate the resistivity and optical characteristics of thefilm, the substrate was heated to 300□ and DC sputtering was performedfor 5 minutes, without marking the substrate with a marker pen.

After deposition had completed, the mark left by the marker pen and thethin film which had accumulated thereon were removed by acetone, and theresulting difference in level, that is the film thickness, was measuredusing a surface roughness tester. The deposition rate was calculated bydividing the film thickness by the deposition time.

The deposition rates which were obtained are shown in Table 1. TABLE 1Atomic Ratio of Resistivity of W/In in Sintered sintered oxideDeposition Rate Oxide (Ωcm) (nm/min) Example 1 0.001 0.9k 48 Example 20.04 0.8k 50 A. Example 3 0.10 0.7k 51 Example 4 0.17 0.5k 53

In order to investigate the characteristics of the obtained thin films,thin films were prepared by performing film deposition for thedeposition times calculated from the deposition rates as necessary toobtain film thicknesses of approximately 300 nm respectively, and thesurface resistance was measured by the four-point probe method in orderto calculate the resistivity. At the same time, the opticalcharacteristics were measured using a spectrophotometer.

The results showed that the resistivity of the thin films was less than1×10⁻³ Ωcm, and the optical transmission was excellent for both thevisible light region and the infrared light region.

Comparative Examples 1 to 4 The Effect of Average Particle Diameter

Oxide sintered bodies were prepared under the same conditions as theexamples 1 through 4, with the exceptions that WO₃ powder with anaverage particle size of between 3 μm and 5 μm was used, that thepowders were mixed at predetermined ratios to obtain the atomic ratiosshown in Table 2, and that the mixing time in the wet ball mill wasshorter, at 5 hours. In addition, the resistivity of the oxide sinteredbodies was measured, the sputtering targets were prepared and DCsputtering was performed, thin films were deposited, and the depositionrates were calculated from the measured film thicknesses, in the samemanner as for the examples 1 to 4.

The resistivity measured for the oxide sintered bodies, and thedeposition rates which were obtained are shown in Table 2.

Analysis by X-ray powder diffraction measurement, a scanning electronmicroscope and EPMA showed that these oxide sintered bodies included aWO₃ phase. Furthermore, the resistivity of the oxide sintered bodies wasbetween 11 kΩcm and 39 kΩcm. TABLE 2 Atomic Ratio of Resistivity of W/Inin Sintered sintered oxide Deposition Rate Oxide (Ωcm) (nm/min) Com.Example 1 0.001 11k 38 Com. Example 2 0.04 23k 37 Com. Example 3 0.1025k 37 Com. Example 4 0.17 39k 34Com. = Comparative

In order to investigate the characteristics of the obtained thin films,thin films were prepared by performing film deposition for thedeposition times calculated from the deposition rates as necessary toobtain film thicknesses of approximately 300 nm respectively, and thesurface resistance was measured by the four-point probe method in orderto calculate the resistivity. At the same time, the opticalcharacteristics were measured using a spectrophotometer.

As a result, the resistivity of the thin films of the comparativeexamples 1 to 4 was approximately 20 to 30% higher than that of the thinfilms obtained in the examples 1 to 4, although it was lower than 1×10⁻³Ωcm in each case, and transmission characteristics were good in both thevisible light region and the infrared light region.

However, a comparison of the deposition rates in Table 1 and Table 2shows that the deposition rates for the examples 1 to 4, which usedsputtering targets prepared from oxide sintered bodies formed from abixbyite structure indium oxide crystal phase and/or an indium tungstatecompound crystal phase, were markedly higher than those for thecomparative examples 1 to 4 which used sputtering targets prepared fromoxide sintered bodies containing a tungsten oxide crystal phase, andthese higher deposition rates are useful in terms of productivity.

Examples 5 to 20 The Effects of the Reduction Process

Next, the oxide sintered bodies composed of indium oxide and containingtungsten according to the examples 1 to 4, which comprise a bixbyitestructure indium oxide crystal phase and an indium tungstate compoundcrystal phase, were subjected to heating and a reduction process(annealing) in a vacuum to control the resistivity. By setting theanneal temperature to 1100□ and varying the annealing time within arange from 1 hour to 10 hours, oxide sintered bodies with a variety ofresistivity values were obtained.

In other words, the oxide sintered body obtained according to theexample 1 was used in examples 5, 9, 13 and 17, the oxide sintered bodyobtained according to the example 2 was used in examples 6, 10, 14 and18, the oxide sintered body obtained according to the example 3 was usedin examples 7, 11, 15 and 19, and the oxide sintered body obtainedaccording to the example 4 was used in examples 8, 12, 16 and 20. Theannealing time was set to 1 hour for the examples 5 to 8, 3 hours forthe examples 9 to 12, 6 hours for the examples 13 to 16, and 10 hoursfor the examples 17 to 20.

X-ray powder diffraction measurement was used to verify that the crystalphases which constitute the oxide sintered bodies remained unchangedafter annealing.

Subsequent to the reduction process (annealing), the oxide sinteredbodies were processed to a diameter of 152 mm and a thickness of 5 mm,and the sputtering surfaces were polished using a cup grindstone. Theresistivity of the sputtering surfaces of the oxide sintered bodies wasmeasured using the four-point probe method.

The measured resistivity values are shown in Table 3.

In addition, after having undergone the reduction process (annealing),the oxide sintered bodies were processed through grinding using the samemethod as the examples 1 to 4, and bonded to a backing plate made ofoxygen free copper, to produce sputtering targets. DC sputtering wasperformed using these sputtering targets under the same conditions asthe examples 1 to 4, and the deposition rates were calculated from themeasured film thickness values.

The deposition rates which were obtained are shown in Table 3. TABLE 3Atomic Ratio of Resistivity of W/In in Sintered sintered oxideDeposition Rate Oxide (Ωcm) (nm/min) Example 5 0.001 10 53 Example 60.04 23 52 Example 7 0.10 43 56 Example 8 0.17 24 54 Example 9 0.001 7 ×10⁻¹ 58 Example 10 0.04 4 × 10⁻² 55 Example 11 0.10 6 × 10⁻¹ 59 Example12 0.17 9 × 10⁻² 58 Example 13 0.001 9 × 10⁻³ 64 Example 14 0.04 6 ×10⁻³ 63 Example 15 0.10 3 × 10⁻³ 62 Example 16 0.17 8 × 10⁻³ 65 Example17 0.001 9 × 10⁻⁴ 65 Example 18 0.04 6 × 10⁻⁴ 67 Example 19 0.10 3 ×10⁻⁴ 65 Example 20 0.17 5 × 10⁻⁴ 65

It is apparent from Table 3 that the lower the resistivity of the oxidesintered body, the more the deposition rate increases. When theresistivity of the oxide sintered body is less than 1×10⁻² Ωcm (theexamples 13 to 20), deposition can be achieved at higher speeds (fasterthan 62 nm/min).

In order to investigate the characteristics of the obtained thin films,thin films were prepared by performing film deposition for thedeposition times calculated from the deposition rates as necessary toobtain film thicknesses of approximately 300 mu respectively, and thesurface resistance was measured by the four-point probe method in orderto calculate the resistivity. At the same time, the opticalcharacteristics were measured using a spectrophotometer.

The results showed that the resistivity of the thin films was less than1×10⁻³ Ωcm, and the optical transmission was good for both the visiblelight region and the infrared light region.

Examples 21 to 28 The Effects of the Reduction Process

Next, the oxide sintered bodies prepared in the comparative examples 1to 4 were heated and subjected to a reduction process (annealing) in avacuum, to control the resistivity. By setting the anneal temperature to1100□ and varying the annealing time within a range from 5 hours to 10hours, oxide sintered bodies with a variety of resistivity values wereobtained.

In other words, the oxide sintered body obtained according to thecomparative example 1 was used in examples 21 and 25, the oxide sinteredbody obtained according to the comparative example 2 was used inexamples 22 and 26, the oxide sintered body obtained according to thecomparative example 3 was used in examples 23 and 27, and the oxidesintered body obtained according to the comparative example 4 was usedin examples 24 and 28. The annealing time was set to 5 hours for theexamples 21 through 24, and 10 hours for the examples 25 through 28.

X-ray powder diffraction measurement was used to verify that the crystalphases which constitute the oxide sintered bodies remained unchangedafter annealing.

Subsequent to the reduction process (annealing), the oxide sinteredbodies were processed to a diameter of 152 mm and a thickness of 5 mm,and the sputtering surfaces were processed through grinding by a cupgrindstone. The resistivity of the sputtering surfaces of the oxidesintered bodies was measured using the four-point probe method.

The measured resistivity values are shown in Table 4.

In addition, after having undergone the reduction process (annealing),the oxide sintered bodies were processed through grinding using the samemethod as the examples 1 to 4, and bonded to a backing plate made ofoxygen free copper, to produce sputtering targets. DC sputtering wasperformed using these sputtering targets under the same conditions asthe examples 1 to 4, and the deposition rates were calculated from themeasured film thickness values.

The obtained deposition rates are shown in Table 4. TABLE 4 Atomic Ratioof Resistivity of W/In in Sintered sintered oxide Deposition Rate Oxide(Ωcm) (nm/min) Example 21 0.001 0.4k 48 Example 22 0.04 0.6k 47 Example23 0.10 0.5k 47 Example 24 0.17 0.8k 47 Example 25 0.001 20 50 Example26 0.04 17 52 Example 27 0.10 25 50 Example 28 0.17 44 49

In order to investigate the characteristics of the obtained thin films,thin films were prepared by performing film deposition for thedeposition times calculated from the deposition rates as necessary toobtain film thicknesses of approximately 300 nm respectively, and thesurface resistance was measured by the four-point probe method in orderto calculate the resistivity. At the same time, the opticalcharacteristics were measured using a spectrophotometer.

The results showed that the resistivity of the thin films was less than1×10⁻³ Ωcm, and the optical transmission was good for both the visiblelight region and the infrared light region.

A comparison of the examples 5 to 8 which do not contain tungsten oxideand the examples 25 to 28 which do contain tungsten oxide showed thatthe resistivity of the oxide sintered bodies is at approximately thesame level, but the deposition rates of the examples 5 to 8 wereslightly faster. Accordingly, it is apparent that the deposition ratecan be improved by using an oxide sintered body comprising a bixbyitestructure indium oxide crystal phase which contains tungsten as a solidsolution, and/or an indium tungstate compound crystal phase (theexamples 5 to 8), which does not contain a tungsten oxide crystal phase,and this is desirable also in terms of productivity.

Furthermore, in oxide sintered bodies composed mainly of indium andcontaining tungsten, oxide sintered bodies which contain a tungstenoxide crystal phase could only lower the resistivity by several dozenΩcmthrough the vacuum annealing process, as seen in the examples 25 to 28.

Accordingly, a low resistance oxide sintered body which enables fastdeposition should be an oxide sintered body comprising a bixbyitestructure indium oxide crystal phase which contains tungsten as a solidsolution and/or an indium tungstate compound crystal phase, which doesnot contain a tungsten oxide crystal phase, as prepared in the examples1 to 4.

Oxide Sintered Bodies Composed Mainly of Indium and Containing Tungstenand Tin

Examples 29 to 44 The Effects of Particle Diameter

Oxide sintered bodies were prepared under the same conditions as theexamples 1 to 4, with the exception that mixtures were prepared usingIn₂O₃ powder, WO₃ powder and SnO₂ powder with average particle diametersof up to 1 μm as the raw materials, which were combined at predeterminedratios to obtain a fixed W/In atomic ratio of 0.10 and to obtain theSn/In atomic ratios shown in Table 5. X-ray powder diffractionmeasurements, a scanning electron microscope and EPMA confirmed thatthese oxide sintered bodies did not include a tungsten oxide crystalphase, and that the oxide sintered bodies comprised a bixbyite structureindium oxide crystal phase containing tungsten and tin as a solidsolution and/or an indium tungstate compound crystal phase and/or anindium stannate compound crystal phase.

Next, the obtained oxide sintered bodies were heated and subjected to areduction process (annealing) in a vacuum to control the resistivity. Bysetting the anneal temperature to 1100□ and varying the annealing timewithin a range from 1 hour to 10 hours, oxide sintered bodies with avariety of resistivity values were obtained.

In other words, oxide sintered bodies with the same atomic ratios wasused in examples 29, 33, 37 and 41, oxide sintered bodies with the sameatomic ratios was used in examples 30, 34, 38 and 42, oxide sinteredbodies with the same atomic ratios was used in examples 31, 35, 39 and43, and oxide sintered bodies with the same atomic ratios was used inexamples 32, 36, 40 and 44. The annealing time was set to 1 hour for theexamples 29 to 32, 3 hours for the examples 33 to 36, 6 hours for theexamples 37 to 40, and 10 hours for the examples 41 to 44.

X-ray powder diffraction measurement was used to verify that the crystalphases which constitute the oxide sintered bodies remained unchangedafter annealing.

Subsequent to the reduction process (annealing), the oxide sinteredbodies were processed to a diameter of 152 mm and a thickness of 5 mm,and the sputtering surfaces were processed thorugh grinding by a cupgrindstone. The resistivity of the sputtering surfaces of the oxidesintered bodies was measured using the four-point probe method.

The measured resistivity values are shown in Table 5.

In addition, after having undergone the reduction process (annealing),the oxide sintered bodies were processed through grinding using the samemethod as the examples 1 to 4, and bonded to a backing plate made ofoxygen free copper, to produce sputtering targets. DC sputtering wasperformed using these sputtering targets under the same conditions asthe examples 1 to 4, and the deposition rates were calculated from themeasured film thickness values.

The obtained deposition rates are shown in Table 5. TABLE 5 Atomic Ratioof Resistivity of Sn/In in Sintered sintered oxide Deposition Rate Oxide(Ωcm) (nm/min) Example 29 0.01 55 52 Example 30 0.05 56 53 B. Example 310.10 50 52 Example 32 0.15 48 53 Example 33 0.01 2 × 10⁻¹ 53 Example 340.05 1 × 10⁻² 54 Example 35 0.10 2 × 10⁻¹ 53 Example 36 0.15 4 × 10⁻² 53Example 37 0.01 5 × 10⁻³ 64 Example 38 0.05 5 × 10⁻³ 64 Example 39 0.104 × 10⁻³ 65 Example 40 0.15 5 × 10⁻³ 64 Example 41 0.01 6 × 10⁻⁴ 68Example 42 0.05 4 × 10⁻⁴ 68 Example 43 0.10 3 × 10⁻⁴ 67 Example 44 0.155 × 10⁻⁴ 67

In order to investigate the characteristics of the obtained thin films,thin films were prepared by performing film deposition for thedeposition times calculated from the deposition rates as necessary toobtain film thicknesses of approximately 300 nm respectively, and thesurface resistance was measured by the four-point probe method in orderto calculate the resistivity. At the same time, the opticalcharacteristics were measured using a spectrophotometer.

The results showed that the resistivity of the thin films was less than1×10⁻³ Ωcm, and the optical transmission was good for both the visible]light region and the infrared light region.

Comparative Examples 5 to 8 The Effect of Particle Diameter

Oxide sintered bodies were prepared under the same conditions as theexamples 1 to 4, with the exceptions that mixtures were prepared usingIn₂O₃ powder and SnO₂ powder with average particle diameters of up to 1μm, and WO₃ powder with an average particle diameter between 3 μm and 5μm, which were combined at predetermined ratios to obtain a fixed W/Inatomic ratio of 0.10 and the Sn/In atomic ratios shown in Table 6, andthat the mixing time in the wet ball mill was shorter, at 5 hours.Analysis by X-ray powder diffraction measurement, a scanning electronmicroscope and EPMA showed that these oxide sintered bodies included aWO₃ phase.

The obtained oxide sintered bodies were processed to a diameter of 152mm and a thickness of 5 mm, the sputtering surfaces were processedthrough grinding using a cup grindstone, and the resistivity of thesputtering surfaces of the oxide sintered bodies was measured using thefour-point probe method.

The measurement results are shown in Table 6. The resistivity of theoxide sintered bodies was between 15 kΩm and 58 kΩcm.

The obtained oxide sintered bodies were then polished using the samemethod as the examples 1 to 4, and bonded to a backing plate made ofoxygen free copper, to produce sputtering targets. DC sputtering wasperformed using these sputtering targets under the same conditions asthe examples 1 to 4, and the deposition rates were calculated from themeasured film thickness values.

The deposition rates which were obtained are shown in Table 6. TABLE 6Atomic Ratio of Resistivity of Sn/In in Sintered sintered oxideDeposition Rate Oxide (Ωcm) (nm/min) Com. Example 5 0.01 58k 34 Com.Example 6 0.05 23k 35 Com. Example 7 0.10 15k 34 Com. Example 8 0.15 60k32Com. = Comparative

The deposition rates achieved when the oxide sintered bodies accordingto the comparative examples 5 through 8 were used as the sputteringtarget were between 32 and 35 nm/min, which is extremely slow incomparison with the examples 29 to 44, and impractical in terms ofproductivity.

Examples 45 to 52 The Effects of the Reduction Process

Next, the oxide sintered bodies prepared in the comparative examples 5to 8 were heated and subjected to a reduction process (annealing) in avacuum, to control the resistivity. By setting the anneal temperature to1100□ and varying the annealing time within a range from 5 hours to 10hours, oxide sintered bodies with a variety of resistivity values wereobtained.

In other words, the oxide sintered body obtained according to thecomparative example 5 was used in examples 45 and 49, the oxide sinteredbody obtained according to the comparative example 6 was used inexamples 46 and 50, the oxide sintered body obtained according to thecomparative example 7 was used in examples 47 and 51, and the oxidesintered body obtained according to the comparative example 8 was usedin examples 48 and 52. The annealing time was set to 5 hours for theexamples 45 through 48, and 10 hours for the examples 49 through 52.

X-ray powder diffraction measurement was used to verify that the crystalphases which constitute the oxide sintered bodies remained unchangedafter annealing.

Subsequent to the reduction process (annealing), the oxide sinteredbodies were processed to a diameter of 152 mm and a thickness of 5 mm,and the sputtering surfaces were processed through grinding by a cupgrindstone. The resistivity of the sputtering surfaces of the oxidesintered bodies was measured using the four-point probe method.

The measured resistivity values are shown in Table 7.

In addition, after having undergone the reduction process (annealing),the oxide sintered bodies were processed through grinding using the samemethod as the examples 1 to 4, and bonded to a backing plate made ofoxygen free copper, to produce sputtering targets. DC sputtering wasperformed using these sputtering targets under the same conditions asthe examples 1 to 4, and the deposition rates were calculated from themeasured film thickness values.

The thus obtained deposition rates are shown in Table 7. TABLE 7 AtomicRatio of Resistivity of Sn/In in Sintered sintered oxide Deposition RateOxide (Ωcm) (nm/min) Example 45 0.01 0.4k 48 Example 46 0.05 0.6k 50Example 47 0.10 0.5k 47 Example 48 0.15 0.8k 47 Example 49 0.01 58 56Example 50 0.05 55 58 Example 51 0.10 54 57 Example 52 0.15 50 55

In order to investigate the characteristics of the obtained thin films,thin films were prepared by performing film deposition for thedeposition times calculated from the deposition rates as necessary toobtain film thicknesses of approximately 300 nm respectively, and thesurface resistance was measured by the four-point probe method in orderto calculate the resistivity. At the same time, the opticalcharacteristics were measured using a spectrophotometer.

The results showed that the resistivity of the thin films was less than1×10⁻³ Ωcm, and the optical transmission was good for both the visiblelight region and the infrared light region.

Although the oxide sintered bodies according to the examples 45 to 52contained a tungsten oxide crystal phase, subjecting these oxidesintered bodies to an annealing process in a vacuum reduced theresistivity to less than 1 kΩcm. Because the deposition rates werefaster for these examples than for the oxide sintered bodies accordingto the comparative examples 5 to 8, this type of oxide sintered body canbe used in production.

A comparison of the examples 29 to 32 and the examples 49 to 52 showedonly that the resistivity of the oxide sintered bodies was atapproximately the same level, and that the deposition rate was slightlyhigher for the examples 49 to 52. Accordingly, it is apparent that theoxide sintered bodies comprising a bixbyite structure indium oxidecrystal phase containing tungsten as a solid solution and/or an indiumtungstate compound crystal phase, which do not contain a tungsten oxidecrystal phase (the examples 29 to 32) are preferable.

In addition, the exact same tendency was observed when the W/In atomicratio of the sintered bodies was altered to 0.001, 0.01, 0.03, 0.07 or0.15 and the Sn/In atomic ratio was varied in the same manner as inTable 6 and Table 7.

In the experiments relating to deposition in the present specification,deposition rates were compared based on sputtering deposition performedwith an introduced DC power of 160 W, but same tendencies were observedwhen the introduced DC power was increased to 300 W and 500 W.Furthermore, the exact same tendencies were observed when deposition wasperformed using an RF sputtering method.

In addition, it was confirmed that an oxide based transparent conductivefilm with the same characteristics as the examples could also beobtained when deposition was performed using an ion plating method.

By using an oxide sintered body of the present invention as a sputteringtarget or an ion plating tablet, because the oxide sintered bodycomprises a bixbyite structure indium oxide crystal phase containingtungsten as a solid solution and/or an indium tungstate compound crystalphase, and does not contain a tungsten oxide crystal phase, a sputteringtarget or an ion plating tablet can be provided which enables depositionto be achieved faster than with conventional targets, and enables themanufacture of a low resistance oxide based transparent conductive film.As a result, it is possible to manufacture quickly low resistance oxidebased transparent conductive films with excellent transmissioncharacteristics for both the visible light region and the infrared lightregion, and low resistance oxide based transparent conductive films withsmooth surfaces, using industrially applicable sputtering methods or ionplating methods, and consequently highly efficient solar cells andorganic EL displays and LCDs with excellent performance can be producedat low cost, and the industrial value of the present invention isreadily apparent.

1. An oxide sintered body consisting essentially of indium and tungsten,and having a resistivity of up to 1 kΩcm.
 2. An oxide sintered body ofclaim 1, wherein the resistivity is up to 50 Ωcm.
 3. An oxide sinteredbody of claim 1, wherein the resistivity is up to 1 Ωcm.
 4. An oxidesintered body of claim 1, wherein the resistivity is up to 1×10⁻² Ωcm.5. An oxide sintered body of claim 1, wherein the resistivity is up to1×10⁻³ Ωcm
 6. An oxide sintered body of claim 1, wherein the tungsten iscontained by an amount from 0.001 to 0.17 in W/In of atomic ratio.
 7. Anoxide sintered body of claim 1, wherein the oxide sintered bodycomprises mainly a bixbyte structure indium oxide crystal phasecontaining tungsten in a solid solution and/or an indium tungstatecompound crystal phase and wherein no tungsten oxide crystal phase iscontained.
 8. An oxide sintered body consisting essentially of indiumand tungsten and tin, and having a resistivity of up to 1 kΩcm.
 9. Anoxide sintered body of claim 8, wherein the resistivity is up to 60 Ωcm.10. An oxide sintered body of claim 8, wherein the resistivity is up to1 Ωcm.
 11. An oxide sintered body of claim 8, wherein the resistivity isup to 1×10⁻² Ωcm.
 12. An oxide sintered body of claim 8, wherein theresistivity is up to 1×10⁻³ Ωcm.
 13. An oxide sintered body of claim 8,wherein the tungsten is contained by an amount from 0.001 to 0.17 inW/In of atomic ratio, and wherein the tin is contained by an amount from0.001 to 0.15 in Sn/In of atomic ratio.
 14. An oxide sintered body ofone of claims 8, wherein the oxide sintered body comprises mainly abixbyte structure indium oxide crystal phase containing tungsten and tinin a solid solution and/or an indium tungstate compound crystal phaseand/or an indium stannate compound crystal phase and wherein no tungstenoxide crystal phase is contained.
 15. An oxide sintered body consistingessentially of indium and either tin or tungsten, and having aresistivity of up to 1 kΩcm.